1. Field of the Invention
The present invention relates to an endoscope that includes a bending portion on a distal end side of an insertion portion and performs bending operation of the bending portion by a bending operation member provided on an operation portion on a hand side.
2. Description of the Related Art
In recent years, endoscopes have been utilized in a medical field and an industrial field. There is an endoscope provided with a bending portion on a distal end side of an elongated insertion portion. In general, a bending operation member provided on an operation portion on a proximal end side of the insertion portion is operated by hand to perform bending motion of the bending portion in a desired direction.
Examples of the bending operation member provided on the operation portion include a bending knob or a bending lever rotated and operated about an axis and a joy stick lever tilted and operated.
The bending portion provided in the insertion portion is covered by bending rubber with elastic force. A plurality of endoscope built-in parts, such as a treatment instrument channel tube, an air feeding tube, a water feeding tube, a signal cable including a bundle of a plurality of signal lines, and an illumination light guide, are inserted and arranged in the insertion portion. The endoscope built-in parts serve as elastic resistances when the bending portion is bent. Therefore, when the bending portion is bent, elastic restoring force (see a solid line L of FIG. 1) for returning the bending portion to a straight line state acts on the bent bending portion due to the bending rubber and the endoscope built-in parts.
Furthermore, when the endoscope is bent, the built-in parts come into contact with each other and generate friction force.
Bending portion resistance force that is a combination of the elastic restoring force and the friction force increases with an increase in a bending angle of the bending portion.
Therefore, when the bending portion is bent, a user operates the bending operation member by bending operation force indicated by a first dashed line L1 of FIG. 1 that is force against the bending portion resistance force. In this case, the bending portion resistance force increases with an increase in the bending angle of the bending portion, and the bending operation force for operating the bending operation member also increases.
As a result, a load on a finger of the user becomes large. When the user temporarily separates the finger from the bending operation member during the operation, the bending angle may be reduced by the elastic restoring force or the like of the bending rubber and the endoscope built-in parts, and the user may lose sight of an observed site.
In order to resolve the trouble, an operation portion of a conventional endoscope is provided with, for example, a semi-fixation mechanism including a lever, a cam mechanism, and a friction plate. The semi-fixation mechanism is a mechanism that makes a switch to a semi-fixation state and a semi-fixation release state, wherein in the semi-fixation state, lever operation brings the friction plate into contact with, for example, a drum to which one end of a bending wire is fixed, and in the semi-fixation release state, the friction plate is separated from the drum.
In the semi-fixation state, the bending portion can perform bending motion along with the operation of the bending operation member. On the other hand, when the user separates the finger from the bending operation member, the bending portion holds a bending state before the separation. Therefore, when the user captures a target observed site, the user selects the semi-fixation state to perform observation and the like while preventing losing sight of the observed site.
Note that the bending operation force for operating the bending operation member varies between first bending operation force indicated by the first dashed line L1, in which the bending angle of the bending portion increases, and bending holding force indicated by a second dashed line 2, in which the bending angle is held in this state, and the bending holding force is smaller than the elastic restoring force.
This is because the bending rubber and the endoscope built-in parts act as restoring force when the bending angle of the bending portion is increasing, and the friction force acts in an opposite direction of the restoring force when the bending angle is held. In other words, to prevent the bending angle of the bending portion from changing when the finger is separated from the bending operation member during the operation of the bending operation member, semi-fixation force (force F with a magnitude indicated by an arrow of FIG. 1) for canceling the bending holding force can be provided from the semi-fixation mechanism to the drum.